1. Field of the Invention
This invention relates to a gas feed pipe connecting screw (hereinafter referred to as “connecting screw”) mounted to a continuous casting nozzle (hereinafter referred to as “nozzle”) formed with an axially extending ring-shaped slit substantially concentric with a nozzle bore for connecting to the nozzle a gas feed pipe blowing a gas into the slit.
2. Description of the Related Art
A nozzle used in continuous casting is formed with an axially extending ring-shaped slit substantially concentric with a nozzle bore in order that inclusion adherent to an inner wall of the nozzle during continuous casting may be eliminated. An inert gas such as argon gas is blown into the slit. A gas feed pipe feeding the inert gas is connected to a connecting screw mounted on a sidewall of the nozzle. JP-2001-219252-A discloses such a connecting screw. A female thread is formed so as to be continuous to a mounting hole of the nozzle side wall. A male thread adapted to be into mesh engagement with the female thread has three or more spot-welded portions w projecting from an outer circumference thereof. The mounting hole is filled with mortar y. The spot-welded portions are caused to engage the mortar y, whereby detent is provided as shown in FIG. 4.
However, each spot-welded portion has a lower detent strength than an integrally formed product. Moreover, a constant detent strength is difficult to obtain by achieving a uniform welding strength of each spot-welded portion, whereupon the detent strength differs from one product to another. As a result, the spot-welded portions would be broken due to high temperature, vibration or the like, so that the connecting screw would fall off from the nozzle. Additionally, a nut having a detent structure is proposed. However, the nut cannot be manufactured readily and the cost of the nut is increased since the nut has a complicated shape.